It is known to provide rotatable and indexable punching tools in a turret punch press where the upper and lower punching tools are rotated synchronously for different orientations of the punch tools. Further, it is known to provide multiple station turret punch machines which provide a large number of different punch stations for use in conjunction with a like number of opposing die surfaces. Each station may include an upper punch assembly and a lower die assembly. The typical configuration of the punch assembly includes a punch tip that is mounted onto the lower end of a punch driver which, in turn, is threadably connected to a punch head.
As illustrated in U.S. Pat. No. 4,375,774, which is incorporated herein by reference, the punch tip can become dull or worn during use. As a result, the tips are routinely sharpened using a grinding operation which shortens the overall length of the punch tip, and accordingly, the overall length of the punch assembly. Because the distance between the cutting edge of the punch tip and the workpiece is a critical dimension, control of the vertical position, and hence the overall length of the punch assembly, is important. U.S. Pat. No. 4,375,774 discloses an adjustable punch assembly whereby the punch driver is threadably attached to the punch head. By rotating the punch driver with respect to the punch head, the overall length of the punch assembly can be shortened or lengthened.
Further, punch presses having indexable tool stations enable the punch assembly, and hence the punch tip, to be rotated so that the punch tip can be applied to the workpiece in different orientations. Punch presses employing indexable punch stations are disclosed in U.S. Pat. Nos. 5,048,385 and 4,658,688, both of which are incorporated herein by reference and both of which are owned by the assignee of the present application.
Specifically, U.S. Pat. No. 4,658,688 discloses a turret punch press having an upper and lower turret tool holder which carries a number of punch and die sets in individual tool holding stations in the turrets. At least one of the corresponding tool holding stations in the upper and lower turrets is indexable to different angular orientations. Rotation of the indexable punch tools is accomplished by a slidably mounted motor for engagement with a timing pulley, which, through a timing belt and harmonic gear drive, acts to rotate the tool holder which carries the punch and die set. In this device, each of the turrets may be equipped with tool stations which receive tool support devices that are rotatable to selectively position the tools at chosen angular positions by rotating the tool sets about their longitudinal axes.
U.S. Pat. No. 5,048,385 discloses a punch assembly for an indexable punching station which includes a striker body having a solid portion and a punch carrier which carries a plurality of individual punches. A selectively actuable stop holds the striker body stationary, allowing the punch holder to be rotated so that one of the plurality of punches will underlie the solid portion of the striker body. The stop may then be deactivated so that the entire punch assembly may be rotated to a variety of angular orientations. Rotation of the assembly thus permits a single punch to be used to punch holes of the same shape but with differing angular orientations.
Thus, U.S. Pat. No. 4,375,774 discloses an adjustable punch assembly whereby the overall length of the punch assembly may be adjusted to accommodate for wear on the punch tip or the shortening of the punch tip due to sharpening or grinding operations. U.S. Pat. Nos. 4,658,688 discloses an indexable tool station which permits the angular rotation of the punching tool. U.S. Pat. No. 5,048,385 expands on this concept by enabling the angular rotation of the entire punch assembly and further angular rotation of a tool holder to thereby selectively dispose a selected punch tool under the solid portion of the striker body.
However, the punch tip disclosed in U.S. Pat. No. 4,658,688 and punch tips generally known in the art are attached to the punch driver by a threaded shaft that passes through axial passageways in both the punch head and the punch driver. The shaft needs to be tightened to a specific torque rating in order to properly retain the punch tip. Thus, changing the punch tip in favor of an alternative punch tip is time consuming and therefore costly. Accordingly, there is a need in the punch press art for punch tips that may be changed more quickly and therefore more economically than currently available punch tips.
Further, while U.S. Pat. No. 4,658,688 discloses a punch assembly having an overall length that may be adjusted by rotating the punch head with respect to the punch driver, the design disclosed in U.S. Pat. No. 4,658,688 requires that any length adjustment be made during the initial installation of the punch tip. There is no way to adjust the overall length of the punch assembly during operation of the punch press. Accordingly, there is a need for an improved punch assembly that may be length adjusted during operation to compensate for tip wear, changes in the workpiece material or other operational variables.